First make the praline. Heat the sugar in a heavy-based saucepan without stirring until it caramalises and turns a golden colour. Add the hazelnuts and pour the praline mixture onto a sheet of greaseproof paper.

Let the praline cool then refrigerate for 2 hours until firm. Using a rolling pin smash the praline into pieces.

Now make the mousse. Heat 200g of the chocolate in a bain-marie (a heatproof bowl suspended over a saucepan of simmering water) until the chocolate has melted.

Add the butter to the melted chocolate and mix in until melted. Beat in the cocoa powder, mixing well.

Whisk the cream until peaks form.

Beat the egg yolks with 50g caster sugar until pale yellow. Beat the egg whites with the remaining sugar until peaks form.

Fold together the chocolate mixture with the egg yolk mixture. Fold in the beaten egg whites, then the whipped cream.

Mix in the broken praline, saving a little for decoration, and the remaining chocolate.

Spoon the mousse into 8 chocolate cups, cover and chill until ready to serve. Sprinkle over the reserved praline just before serving.